Several different tests, most of them blood tests, are used not only to diagnose diabetes but to monitor it.
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The American Diabetes Association recommends that all individuals ages 45 and older, particularly those with a body mass index, or BMI, equal to or greater than 25, should be screened for diabetes—and if the test is normal, that they should be retested every three years. Testing should be conducted at earlier ages and carried out more frequently in individuals who have any of the diabetes risk factors.
The ADA recommends that patients should be told they have diabetes if any of the criteria below applies:
- Blood glucose levels as measured by a fasting plasma glucose test are equal to or greater than 126 mg/dl.
- Diabetes symptoms exist and glucose levels measured at random are equal to or above 200 mg/dl.
- Glucose is equal to or greater than 200 mg/dl during an oral glucose tolerance test.
- If test results indicate diabetes, testing should be repeated on a different day to confirm the diagnosis. If a random blood test has found glucose equal to 200 mg/dl or above, the confirming test used should be a fasting plasma glucose or an oral glucose tolerance test.
This section has information on screening tests for diagnosing diabetes.
Diabetes may be diagnosed using the oral glucose tolerance test (OGTT) or a fasting plasma glucose test.
The OGTT requires a fast of eight to 12 hours, after which a person's blood glucose is measured before drinking a glucose-containing solution and then again two hours later. In normal glucose tolerance, blood glucose rises no higher than 140 mg/dl two hours after the drink. In people with prediabetes or impaired glucose tolerance (IGT), the two-hour blood glucose is between 140 and 199 mg/dl. If the two-hour blood glucose rises to 200 mg/dl or above, the diagnosis is diabetes.
In the fasting plasma glucose test, a person's blood glucose is measured once after a fast of eight to 12 hours. A person with normal blood glucose has a blood glucose level below 100. A person with impaired fasting glucose has a blood glucose level between 100 and 125 mg/dl. If the fasting blood glucose level rises to 126 mg/dl or above, the person has diabetes.
The OGTT includes measures of blood glucose levels after a fast and after a glucose challenge. In 1997, an American Diabetes Association expert panel recommended that doctors use the fasting plasma glucose test to screen their patients for diabetes because the test is easier and less costly than the OGTT. On the other hand, the OGTT is more sensitive in identifying people with problems that may first appear only after high glucose intake.
There are two major ways to monitor your diabetes: Have your A1C checked by your healthcare provider, and check your own blood glucose values.
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- Home blood glucose monitoring, which tells you your blood glucose level at that very moment
- A1C testing, which tells you and your healthcare provider about your blood glucose control over the past two to three months
- The fructosamine test, a tool for measuring how well your diabetes treatment program is working
Home blood glucose monitoring provides a snapshot of how your treatment is working at one moment in time, so you can better tailor your eating program and medication. It also tells you if any symptoms you are experiencing, such as sweats or feeling faint, are the result of low blood glucose (hypoglycemia), so you can treat this problem swiftly. When you are sick or under stress, careful monitoring helps you adjust your treatment program immediately to keep your blood glucose level from going too high or too low.
Your doctor or diabetes team will help you decide what type of meter to buy. Most new meters today read the glucose level as if the blood sample were plasma rather than whole blood, since that's the way results are reported by your doctor's office or lab. By having the meter record results as "plasma glucose," you and your healthcare team can more easily compare your lab tests with your home tests. Plasma numbers run 10 to 12 percent higher than those for whole blood; if your premeal plasma glucose target is 90 to 130 mg/dl, the target would be 80 to 120 mg/dl if your meter reads whole blood.
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In order to get an accurate blood glucose result, you need to make sure that the meter is clean, that its code matches your test strips, that your finger is clean, and that you're testing an adequate-size drop of blood. Before pricking your finger, wash your hands with warm water, shake your hands below your waist, and squeeze your finger a few times.
In order to understand what the readings mean for you, you will need to know:
- Your target blood glucose range. A range of 90 to 130 mg/dl before meals is suggested for most people with diabetes. Ask your doctor what your target range should be.
- When to check your blood glucose. Some people check two times a day every day; others check four times a day. Ask your healthcare provider for guidance.
- It's a good idea to write down your blood glucose numbers in a diary or logbook and look for patterns over time. For example, are your blood glucose readings before breakfast higher or lower than your target? Once you see patterns, you can look for causes—and avoid them.
If home blood glucose monitoring is like a snapshot, A1C testing, handled by a lab, is more like a full-length movie; it provides an average of your blood glucose levels over a period of two to three months by measuring how much glucose has combined with the oxygen-carrying hemoglobin in your red blood cells. For people who have not undergone any major changes in their lifestyle or diabetes regimen, A1C tests offer an assessment of long-term blood glucose control. A normal reading would be 4 to 6; in people with diabetes, the target is below 7.
A terrific result does not necessarily mean that your blood glucose has been continuously under control; people with highs and lows that balance each other out could also get a great reading. This is why daily blood glucose readings are so important. A reading that falls between 7 and 8 for more than six months, or a reading over 8, suggests that the treatment plan needs to be changed.
Measuring the amount of fructosamine in the blood allows the healthcare team to assess how well controlled blood glucose levels have been over the past two to three weeks. It is often prescribed when changes are being made in a diabetes treatment plan and information is needed about how well the new plan is working.
Ketones are acids produced when the body burns fat for energy. They are also produced when you lose weight or when insulin is not available to help your body use sugar for energy. When the body is unable to use glucose for energy, it breaks down fat instead; as a result, ketones form in the blood and spill into the urine. These ketones can make you very sick.
You can test to see if your body is making ketones by doing a simple urine test. There are several products available for ketone testing that can be purchased without a prescription. Common product names include Ketostix, Chemstrip K, and Acetest. The test result can be negative or show small, moderate, or large quantities of ketones.
You should test for ketones:
- Anytime your blood glucose is over 250 mg/dl for two checks in a row.
- When you are ill. Often illness, infections, or injuries will cause sudden high blood glucose, and this is an especially important time to check for ketones.
- When you are planning to exercise and the blood glucose is over 250 mg/dl.
- If you are pregnant, you should test for ketones each morning before breakfast and anytime the blood glucose is over 250 mg/dl.
- As long as blood glucose levels are not too high, the presence of ketones is not a problem; this may occur if you are trying to lose weight.
- Untreated high blood glucose with ketones can lead to a life-threatening condition called diabetic ketoacidosis (DKA). If the ketone test is positive, call your diabetes educator or physician to see if you need more insulin, and drink plenty of water and noncaloric fluids to "wash out" the ketones. Continue testing your blood glucose every three to four hours, testing for ketones if the blood glucose is over 250 mg/dl. Do not exercise if your blood glucose is over 250 mg/dl and ketones are present.
Last reviewed on 11/10/2008
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